The present invention relates to a vertebral rod for a spinal osteosynthesis instrumentation, this rod having a constant diameter throughout its length and being adapted to receive bone anchorage implants, and to the osteosynthesis instrumentation including at least one of said rod.
In these instrumentations, the implants anchored in the bone (screws or hooks) have surfaces adapted to the diameter of the rod employed. In many instrumentations, the rods shaped to the anatomy of the vertebral segments on which they must be installed, remain rigid, as described in the French patent 83 07 450 (2 545 350).
However, in some cases, a variable stiffness may be found desirable, the vertebral rod being for example rigid in one part of its length and relatively flexible in the other part. Thus the European patent EP-A-0 612 507 describes a lumbo-sacral instrumentation comprising rods formed by a rigid part and a flexible terminal part which has a diameter less than that of the rigid part. This arrangement permits in this particular case overcoming the difficulties caused by the existence of a "neohinge" ("neocharniere") between the welded vertebrae and the first superjacent vertebra. This solution however requires the use of different implants for each of the two parts of the rod since these implants must indeed be adapted to different diameters of the rod, which involves additional constraints and cost.